Transmissions

ABSTRACT

A combined powershift transmission and main clutch assembly for a vehicle includes a casing containing an input shaft and an output shaft. A planetary transmission is disposed within the casing and is co-axially mounted around the input shaft. The planetary powershift unit includes a sun gear and an annulus gear interconnected by one or more planet gears carded on a planet carder. A first one of the sun gear, the annulus gear, and the planet carder is connected to the input shaft, while a second one of the sun gear, the annulus gear, and the planet carder acts as an output member of the planetary powershift unit. A first clutch is disposed within the casing and co-axially surrounds the output shaft for drivingly connecting the output member of the planetary powershift unit with the output shaft. A second clutch is disposed within the casing and co-axially surrounds the input shaft for selectively clutching a third one of the sun gear, the annulus gear, and the planet carder for co-rotation with one of the first element of the planetary powershift unit, the second element of the planetary powershift unit, and the casing so as to select an operative gear ratio of the powershift unit. A power-take off shaft is connected to the input shaft and extends co-axially therefrom within the output shaft.

This invention relates to transmissions and in particular, though notexclusively, to transmissions for use in tractor drive lines.

It is well known to use a planetary powershift gear unit as one elementin a series connection of units which together form a tractortransmission. It is also well known to use a multi-plate oil-immersedclutch as a main transmission drive clutch in tractor applications.

It is an object of the present invention to provide a combinedpowershift and main clutch assembly which is suitable for use in atractor drive line and which is particularly compact, reliable andreadily installed in an existing tractor transmission housing.

SUMMARY OF THE INVENTION

A combined powershift and main clutch assembly for a vehicletransmission comprising a casing containing:

an input shaft,

an output shaft,

a planetary powershift unit coaxially mounted around the input shaft anddriven therefrom,

a main multi-plate clutch coaxially surrounding the output shaft fordrivingly connecting an output member of the powershift unit with theoutput shaft, and

a power-take-off shaft connected to the input shaft and extendingcoaxially within the output shaft.

The powershift unit preferably includes a secondary clutch meanscoaxially surrounding the input shaft within the casing for selectingthe operative ratio of the powershift unit.

The powershift unit may comprise a sun gear and an annulus gear inter-connected by one or more planet gears carried on a planet carrier, oneelement of the said sun, annulus or carrier being connected to the inputshaft, a second element of said sun, annulus or carrier acting as theoutput member of the powershift and the third element of said sun,annulus or carrier being clutchable by the secondary clutch means eitherfor co-rotation with the first or a second element or to the casing ofthe assembly.

The carrier is preferably connected to the input shaft, the annulus gearacts as the output member of the powershift and the sun gear surroundsthe input shaft and is clutchable by the secondary clutch means toeither the carrier or the casing.

The carrier is preferably splined onto the input shaft by a sleeveportion which surrounds the input shaft, the power take off shaft alsobeing splined to the same sleeve portion.

The secondary clutch means may conveniently comprise a first clutchwhich is spring-engaged to drivingly connect said third element to saidfirst or second element to provide the unitary or lock-up condition ofthe powershift unit and a second hydraulically-engaged clutch whichclutches said third element to said casing to provide a planetary ratioof the powershift unit.

The main multi-plate clutch is preferably engaged by an annular pistonwhich surrounds the output and power-take-off shafts.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the present invention will now described, by way of anexample only, with reference to the accompanying FIG. 1 which is avertical section through a tractor transmission assembly embodying thepresent invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, a tractor transmission assembly 10 comprises atwo-speed planetary powershift unit 11 coaxially mounted around inputshaft 12 which is driven directly from an engine flywheel 13. A mainmulti-plate oil-immersed clutch 14 coaxially surrounds a hollow outputshaft 15 within which a power-take-off (pto) shaft 16 extends. Outputshaft 15 is connected to further transmission stages, for example, asynchromesh gearbox (not shown), to complete the tractor transmission.

The 2-speed powershift unit 11 comprises an input member in the form ofa planet carrier 17 which is splined onto input shaft 12 via a sleeveportion 52, carrier 17 carries planet gears 18 which mesh with a sungear 19 which rotatably surrounds the input shaft 12 and also withannulus gear 20, which acts as the output member of the powershift unit.

The operative ratio of the powershift unit is changed by a secondaryclutch means in the form of a first clutch 22 which is spring engagedand a second clutch 23 which is hydraulically engaged. The first andsecond clutches are interlinked by a common clutch member 24 which formspart of both clutches.

Common clutch member 24 is supported on carrier 25 which is splined ontosun gear 19. Clutch discs 26 are splined onto a sleeve 27 which is inturn splined onto input shaft 12. Thus clutch discs 26 are in effectconnected with planet carrier 17 via input shaft 12. The first clutch 22is completed by a further clutch disc 28 which is splined onto carrier25 and a belleville spring 29 which biases the common clutch member 24against the interleaved clutch discs 26, 28 in order to connect theplanet carrier 17 with the sun gear 19 to lock-up the powershift unitand provide a first unitary ratio of the unit.

The second clutch 23 comprises the common clutch member 24 which can beclutched to the casing 30 of the assembly between clutch discs 21, whichare carried on the casing, by an annular piston 31 which is displaced bypressurising a chamber 32 via a passageway 33. Normally the secondclutch 23 is held disengaged by return springs 34, as shown in the tophalf of the drawing. When chamber 32 is pressurised, the common clutchmember 24 is gripped between the piston 31 and the housing 30 to clutchthe sun gear 19 to the casing via carrier 25 in order to provide theplanetary ratio of the powershift unit 11.

As will be appreciated, because the clutch member 24 is common to boththe first and second clutches, when the second clutch is engaged themovement of the common clutch member 24 compresses belleville spring 29and automatically disengages the first clutch 22, as shown in the bottomhalf of the accompanying drawing.

Main clutch 14 comprises a first set of clutch discs 40 which arerotationally connected to an extension 41 of annulus gear 20 and asecond set of clutch discs 42 which are splined onto a sleeve 43 whichis itself splined onto output shaft 15. A pressure plate 44 is retainedon sleeve 43 by a circlip 45 and the clutch is engaged against theaction of spring 46 by an annular piston 47, which surrounds the outputshaft 15. Piston 47 is axially displaced to engage the clutch bypressurising chamber 48 via passageway 49, 50, 51.

The power-take-off shaft 16 which extends within the hollow output shaft15 is splined onto the sleeve portion 52 of the planet carrier 17, sothat the power-take-off shaft is directly driven from the input shaft 12via sleeve portion 52.

The entire transmission assembly is contained within casing 30, which iscontinually supplied with oil for lubrication/cooling via inlet 53. Ascan be seen from the drawing, the oil supplied via inlet 53 flows asindicated by arrows 54 to lubricate/cool the various components of theassembly. Oil leaves the casing via apertures not in the plane of FIG. 1to maintain an oil level typical as shown by dotted line X in tractortransmission housing 56. Bolts (not shown) secure casing 30 to a flange55 provided within housing 56.

An electro-magnetic speed sensor 57 is provided which co-operates withteeth 58 provided on the outside of annulus gear.20 to provide anindication of transmission speed to a control system (not shown) for thetransmission assembly and associated tractor.

The transmission assembly described above is particularly compact due tothe small size of the sun gear 19 which enables the necessary planetaryratio of say 1:1.18 to 1:1.50 of the powershift unit to be achievedusing a single epicyclic gear train without excessive diameter of theannulus gear 20. This small diameter of the sun gear 19 is achieved asthe input shaft is connected to the pro shaft so that sun gear 19 isonly required to surround the input shaft 12 and not, as is common inmost tractor applications, to surround a hollow (and therefore largerdiameter) output shaft down the centre of which a power-take-off shaftalso extends. This obviates the need to use a compound epicyclic geartrain to achieve the desired small planetary ratio without excessivegear diameter.

Also, the provision of a multi-plate oil-immersed main clutchimmediately adjacent to the powershift unit and contained within thesame housing 30 further significantly improves the practicality of theoverall assembly which, due to its coaxial input and output shafts, caneasily be installed within an existing tractor transmission housing toconvert an existing tractor transmission to powershift/wet clutchoperation. The positioning of the main clutch on the output side of thepowershift unit also reduces the inertia which any synchronizers in thefurther transmission stages connected with output shaft 15 have toabsorb.

What is claimed is:
 1. A combined powershift transmission and clutchassembly for a vehicle comprising:a casing containing an input shaft andan output shaft; a planetary powershift unit disposed within said casingand co-axially mounted around said input shaft, said planetarypowershift unit including a sun gear and an annulus gear interconnectedby one or more planet gears carried on a planet carder, a first elementof said sun gear, said annulus gear, and said planet carrier beingconnected to said input shaft, a second element of said sun gear, saidannulus gear, and said planet carrier acting as an output member of saidpowershift unit; a first clutch disposed within said casing andco-axially surrounding said output shaft for drivingly connecting saidoutput member of said planetary powershift unit with said output shaft;a second clutch disposed within said casing and co-axially surroundingsaid input shaft for selectively clutching a third element of said sungear, said annulus gear, and said planet carrier for co-rotation withone of said first element of said planetary powershift unit, said secondelement of said planetary powershift unit, and said casing so as toselect an operative gear ratio of said planetary powershift unit; and apower-take off shaft connected to said input shaft and extendingco-axially therefrom within said output shaft.
 2. The combinedpowershift transmission and clutch assembly defined in claim 1 whereinsaid planet carrier is connected to said input shaft.
 3. The combinedpowershift transmission and clutch assembly defined in claim 1 whereinsaid annulus gear acts as said output member of said powershift unit. 4.The combined powershift transmission and clutch assembly defined inclaim 1 wherein said second clutch selectively clutches said sun gearwith either said planet carrier or said casing.
 5. The combinedpowershift transmission and clutch assembly defined in claim 1 whereinsaid carrier is splined onto said input shaft by a sleeve portion whichsurrounds said input shaft.
 6. The combined powershift transmission andclutch assembly defined in claim 5 wherein said power take off shaft issplined to said sleeve portion.
 7. The combined powershift transmissionand clutch assembly defined in claim 1 wherein said second clutchincludes a first and second clutch portions, said first clutch portionbeing spring-engaged to drivingly connect said third element of saidplanetary powershift unit to either of said first and second elements ofsaid planetary powershift unit, said second clutch portion beinghydraulically-engaged to clutch said third element of said planetarypowershift unit to said casing.
 8. The combined powershift transmissionand clutch assembly defined in claim 1 wherein said first clutch is amulti-plate clutch which is engaged by an annular piston which surroundssaid output shaft.
 9. The combined powershift transmission and clutchassembly defined in claim 1 wherein said casing defines an interiorwhich is supplied with oil.
 10. A combined powershift transmission andclutch assembly for a vehicle comprising:a casing; an input shaft and anoutput shaft extending through respective input and output portionsdefined thereby within said casing; a planetary powershift unit disposedwithin said input portion of said casing and co-axially mounted aroundsaid input shaft, said planetary powershift unit including a sun gearand an annulus gear interconnected by one or more planet gears carriedon a planet carrier, a first element of said sun gear, said annulusgear, and said planet carrier being connected to said input shaft, asecond element of said sun gear, said annulus gear, and said planetcarrier acting as an output member of said powershift unit; a clutchdisposed within said output portion of said casing and co-axiallysurrounding said output shaft for drivingly connecting said outputmember of said planetary powershift unit with said output shaft; and apower-take off shaft connected to said input shaft and extendingco-axially therefrom within said output shaft.
 11. The combinedpowershift transmission and clutch assembly defined in claim 10 whereinsaid clutch is a first clutch, and further including a second clutchdisposed within said casing and co-axially surrounding said input shaftfor selectively clutching a third element of said sun gear, said annulusgear, and said planet carrier for co-rotation with one of said firstelement of said planetary powershift unit, said second element of saidplanetary powershift unit, and said casing so as to select an operativegear ratio of said planetary powershift unit.
 12. The combinedpowershift transmission and clutch assembly defined in claim 11 whereinsaid planet carrier is connected to said input shaft.
 13. The combinedpowershift transmission and clutch assembly defined in claim 11 whereinsaid annulus gear acts as said output member of said powershift unit.14. The combined powershift transmission and clutch assembly defined inclaim 11 wherein said second clutch selectively clutches said sun gearwith either said planet carrier or said casing.
 15. The combinedpowershift transmission and clutch assembly defined in claim 11 whereinsaid carrier is splined onto said input shaft by a sleeve portion whichsurrounds said input shaft.
 16. The combined powershift transmission andclutch assembly defined in claim 15 wherein said power take off shaft issplined to said sleeve portion.
 17. The combined powershift transmissionand clutch assembly defined in claim 11 wherein said second clutchincludes a first and second clutch portions, said first clutch portionbeing spring-engaged to drivingly connect said third element of saidplanetary powershift unit to either of said first and second elements ofsaid planetary powershift unit, said second clutch portion beinghydraulically-engaged to clutch said third element of said planetarypowershift unit to said casing.
 18. The combined powershift transmissionand clutch assembly defined in claim 11 wherein said first clutch is amulti-plate clutch which is engaged by an annular piston which surroundssaid output shaft.
 19. The combined powershift transmission and clutchassembly defined in claim 11 wherein said casing defines an interiorwhich is supplied with oil.